In the preparation of an electron circuit element having a fine pattern such as semiconductor element, magnetic bubble memory element and the like, a photosensitive resin coating is first applied, by means of a spin coating or the like, on the surface of a base plate to be processed. Then, the coating is exposed, through a pattern mask, to an actinic radiation and developed in a developer, thereby obtaining a resist pattern utilizing a solubility difference between the exposed and the unexposed resin.
In a recent pattern development, the so-called dry etching method, which is quite suitable for the preparation of fine pattern, is often used.
In order to obtain a resist pattern having a highly improved resolving power by a dry etching development technique, it is quite important to use a photosensitive material which shows a big discrepancy in properties between the dry etching resistance at the portion to be retained and brittleness at the portion to be removed at the etching step.
For example, in Japanese Patent Publication (unexamined) No. 127645/90, there is disclosed a method for preparing a resist pattern having an excellent dry etching resistance by utilizing a selective silylation of active hydrogen of Novolak type resin with a comparatively large silicone containing functional group of --Si(CH.sub.3).sub.3.
More concretely, a photosensitive resin having in its molecule an aromatic ring structure with a phenolic hydroxyl group, is applied on a base plate.
Then, the thus formed coating is irradiated with actinic rays in two separate stages, each time using actinic rays each having different wave lengths, thereby forming the coating capable of showing, when subjected to silylation with a hexamethyl disilazane vapor, a big contrast in the dry etching resistance and brittleness in the subsequent dry etching. The desired fine pattern is thus obtained.
In Japanese Patent Publication (unexamined) Nos. 231330/88 and 231331/88, there is disclosed a method wherein a fine pattern is obtained by using a highly sensitive, double-layered positive type resist having an excellent dry etching resistance. For example, in Japanese Patent Publication (unexamined) No. 231330/88, there is disclosed a method wherein an organic resin first layer is applied on a base plate and then a second layer of positive type resist comprising a silicone modified alkali-soluble resin, partial ladder type silicone resin and quinone diazide compound is coated thereon. The thus formed material is exposed through a pattern to actinic rays, the second resist layer is developed with an alkali developer and finally the first organic resin layer is subjected to dry etching to obtain a fine pattern.
However, in the abovementioned selective silylation method, the silylation at the resin portion to be silylated is not so perfect that there is a problem in silylation selectivity in the exposed and the unexposed portions, resulting in deficient dry etching resistance at the unexposed portion, which is unfavorable in obtaining the desired fine pattern.
Moreover, even if the two step exposure technique with actinic rays having different wave lengths has been adopted for the contrasted silylation, the silylation itself is not so effectively done and therefore, additional two step exposure must be used.
Thus, the exposure step is very complicated.
The two layered positive type resist has such problems that the resist must be applied two times and nevertheless the expected dry etching resistance is still not obtained.
It is, therefore, an object of the present invention to provide a method for forming a fine pattern with simple and easy operational steps, in which a resist coating having excellent dry etching resistance is formed on the spot and utilized.